Coating application workspace structures, such as paint spray booths, may often be used in applying sprayed surface coatings to objects such as automobiles, or other vehicles such as aircraft, trains, trucks, buses, watercraft and so on. The purpose of applying a surface coating may tend to be both functional and aesthetic. That is, the coating may tend both (a) to protect the underlying object, whether from corrosion or abrasion, or some other environmental effect, and (b) particularly when employing a pigment, or multiple adjacent layers of different pigments, to vary the appearance of the object.
A coating, in particular a pigmented coating, may be applied to the object in a spray booth. In general, a spray apparatus may tend to emit a very fine spray of paint (or such other coating as may be applied with the sprayer), with the spray being directed by the operator in the general direction of the object to be painted. However, not all of the paint (or other spray) may necessarily encounter and wet the surface of the object to be coated. Inasmuch as the droplets in the spray vary in diameter, and inasmuch as the droplet size may be very small, a portion of the spray mist may remain suspended in the adjacent gas (typically, air) that drifts about inside the spray booth. As the cloud-like mist moves, the small droplets may coalesce and precipitate, leaving unsightly droplets, such as may tend to mar the uniformity of the surface. That is to say, if nothing further is done, it may be that suspended paint overspray may collect on the surface of the object to be coated (such as, for example, an automobile) in a manner that diminishes the quality of the surface coating.
It may be advantageous for a spray booth to have a ventilation system to urge the overspray mist, and other possible contaminants, away from the object to be coated, and, further, it may be advantageous then to purge the extracted overspray. In providing such a ventilation system, it may be desirable to filter the incoming gas, to prevent contaminants from coming into the spray booth, and to filter, or scrub, the outgoing gas to extract the overspray droplets or other suspended particles before exhausting the scrubbed gas.
It may also be advantageous to employ a relatively large volumetric flow of gas during the spraying operation. That is to say, it may be advantageous for the gas exchange rate for a booth 14 ft wide, 9 ft high, and 24 ft long to be of the order of 8,000–16,000 cfm, or more narrowly, 12,000 to 14,000 cfm, or roughly 3–4 air exchanges per minute. The general idea is to draw away the overspray before it can harm the finish. As described herein, it may also be advantageous to employ a gas flow system to aid in curing the surface coating after spray application of the coating, or one or more layers thereof, has taken place.
In one embodiment of downdraft airflow system as described herein, it is thought that differential airflow in the spray booth may be advantageous, as will be explained more fully hereinbelow. In general, it may be desirable to have the highest rate of local gas exchange most closely adjacent to surfaces upon which droplets of overspray might otherwise tend to land.
It may be advantageous to employ a spray booth that is an enclosed structure, which may be sealed. Paint may be applied to an object with a sprayer within the spray booth. In a spray painting operation, some of the paint may become suspended in the air adjacent to the object to be sprayed. A sealed spray booth may tend to discourage the suspended paint from escaping to the ambient air outside the booth. Filtered downdraft or crossdraft airflow, namely air forced to flow down and around, or across, an object and exhausted through a vent, may help in purging suspended paint. This may then tend to aid in the coating of the object, and in discouraging coalesced droplets from precipitating onto the surface of the object inappropriately.
Appropriate lighting inside the booth may tend to be helpful to aid in the application of the surface coating to the object being painted. A better lighting arrangement may provide more complete and uniform lighting, tending to reduce shadowed areas and to illuminate portions of the object that may not otherwise receive adequate lighting. It would be advantageous to have a lighting arrangement for a paint spray booth that might tend to provide enhanced lighting inside the booth, such as might bathe an object in light.
To this end, it may be advantageous to employ a generally convergent lighting system, with sources of illumination sited at a spacing distance greater than the width of the objects typically to be subject to spray coating. It may also be desirable to combine that source of illumination with a system of ventilation that may tend to urge airborne spray droplets away from the sources of illumination.
In the view of the present inventors, to the extent that a non-uniform purging gas distribution system is employed, it may also be advantageous to employ a lighting system in a manner that may tend to take advantage of the non-uniform air distribution pattern, and that may tend to dray the overspray away from the lighting to some extent. That is, it may also be advantageous to discourage overspray deposition on the lighting. Thus, a need exists for an apparatus, and a method for tailoring the purging gas (i.e., air) distribution within the booth, such as may assist in entrainment of overspray paint mist and other particulates, and advantageously to complement such a non-uniform air distribution by the placement of lighting apparatus to enhance the visibility of an operator engaged in the spray coating.